Zodiacal dust bands: Their relation to asteroid families

Abstract

A mathematical model of the spatial distribution of orbitally evolved collisional debris which reproduces the zodiacal dust band phenomenon is developed. The resultant torus has maxima in particle density at heliocentric latitudes near the mean proper orbital inclinations of its constituent particles, and near the loci of perihelia and aphelia of the particle orbits. These perihelion and aphelion band pairs are found to have latitudinal and radial separations which are functions of the orbital elements ( a, e, i) of the constitutent particles, as well as the dispersions in those elements. Models of dust tori associated with seven asteroid families are generated and compared with observations of the principal dust bands. It is found that models of Themis and Koronis dust tori are consistent with the innermost observed bands, α and β, respectively. The γ band particles (seen at ∼8.°3 ecliptic latitude) are best fit by an Eos family model having a dispersion in orbital inclination of ∼1.°4, compared to a value of ∼0.°7 for the Eos family asteroids. Dispersions in orbital elements for the smal dust torus particles (10–100 μm) are expected to be larger than the asteroid population due to a greater frequency of relevant collisions among the former. Other detected dust bands are not found in association with other major asteroid families with the possible exception of the Io family. This suggests that dust bands are not associated solely with local peaks in the volume density of known asteroids, as would be expected from a mechanism uniformly eroding the asteroid population as a whole, but rather supports the theory that they were produced as a consequence of large random collisions among individual asteroids (the largest of which also resulted in observable asteroid families). Such nonequilibrium models are further supported by evidence that the Koronis family has a greater dust population than the larger Themis family. Nonequilibrium models of dust band production and evolution offer a framework within which all dust band observations can be understood. Within this framework, it is found that both Themis and Eos asteroid families are much older than the Koronis family. Dust band particles appear not to have experienced any large orbital decay (less than a few tenths of an AU) due to Poynting-Robertson drag.